Traditionally ink is applied to a roller in a thick film, modulated with a plurality of laterally disposed regulating means to desired thickness and then transferred sequentially to a large number of rollers to thin the ink film and attenuate it to a thickness suitable for application to the image [printing plate] to be printed.
Research work of the American Newspaper Publishers Association [ANPA] has demonstrated an anilox drum dispensing system will produce satisfactory inking of the image without the need of lateral regulating means and the plurality of rollers. Additional benefits are also realized.
An anilox drum is a cylindrical drum having its periphery populated with recessed cells which for publication printing are 11 to 19 microns, ie. 0.000429 to 0.000741 inches, in depth and have a population of 40,000 to 160,000 cells per square inch of the drum's periphery. The cells may have various shapes usually depending upon the processing method of forming the cells.
Universally, past and current practice of dispensing ink with an anilox drum is to immerse the drum in a body of ink to fill the cells with ink and to wipe the excess ink from the drum's periphery with a doctor as the drum is rotated, thus leaving only the ink in the cells for application to the image for printing.
This technique has been plagued with several problems when utilized for publication presses operating at 2000 to 3500 feet per minute surface speed.
Cells of the drum are not consistantly refilled with ink because when the ink is transferred from the cells it is replaced with air and the ink having a high surface tension bridges ove the cells when the cells are submerged in the body of ink. The result is unacceptable non-uniform and inconsistant print quality. U.S. Pat. No. 4,158,333 assigned to the ANPA represents one of many efforts to solve the problem.
Another problem is the ink having a high tack collects dust and fibres from the sheet being printed. This foreign material is transferred from the image to the anilox drum and cloggs cells, contaminates the ink supply and lodges at the interface of the doctor and the drum causing irregular wiping of the drum thereby producing streaking and unacceptable printing. Efforts to relieve this problem are to dilute the contaminated ink body in which the drum is immersed by recirculation and mixing with clean ink.
U.S. Pat. No. 4,373,443 asserts that anilox ink dispensing may be retrofitted to existing printing presses having conventional ink trains and dispensing equipment. While this is possible it is costly and requires taking the press out of production for extended periods of time to effect the retrofit.
Further, prior to the present invention arrangements were not applicable to color decks and color couples which have the printing cylinders located below the ink dispensing means. The inability to fully retrofit existing presses has circumvented the utilization of anilox ink dispensing.